Why do I need to avoid light?

Learn why avoiding light is important, what light to avoid and how to avoid it.

Written by Jacob Ravn Updated over a week ago

What to do when we tell you to avoid light

Minimize light exposure as much as possible. Sunlight (even on a cloudy day) and blue-enriched, cool-looking white light, found in some buildings and emitted by your electronic devices, are the worst. Wearing dark sunglasses at this time will help reduce your light exposure.

When flying:It’s important you avoid light. Lower the window shade if it’s light outside, turn off the overhead light, turn off the TV, and stop using your laptop or tablet. Wearing dark sunglasses will help you avoid unintended light exposure.

Why do I need to avoid light?

Light is the most powerful influence on circadian rhythms. Seeing light at the wrong time can shift circadian rhythms in the wrong direction and make jet lag worse. The plan depends on the balance between light exposure and light avoidance. The recommendations to avoid light are carefully timed and need to be followed as closely as possible.

What kind of light should I avoid?

The effects of light depend on the intensity and spectrum of light. Sunlight is the strongest source of light so do what you can to avoid natural light when you are asked to. Blue-enriched, cool-looking white light, found in some buildings and emitted by your electronic devices, are the worst. Wearing sunglasses will help reduce the light exposure to your eyes.

What will happen to my jet lag if I don’t avoid light?

If you can’t follow the plan perfectly, don’t give up. Just do the best you can. If you can’t avoid light when recommended, it will take longer to overcome your jet lag.

What are the most effective sunglasses?

All visible light can affect the circadian rhythm so use sunglasses that are as dark as possible to block the most light. ‘Wrap-around’ styles will help reduce light exposure further. “Blue-blocking” glasses can also be used but these will likely not be as effective as sunglasses, especially at lower light levels.

The Science

Light is the most important factor in resetting your circadian rhythm — the disruption of the light-dark cycle is in fact what causes jet lag in the first place. Light resets our circadian rhythm to 24 hours each and every day, and is detected by special photoreceptors in the eye.

Light can shift the clock earlier (called an advance) or later (called a delay) depending on the timing of light. This relationship is described by a “phase response curve”. Generally speaking, light exposure in the evening or early night will delay the clock, and light in the late night or early morning will advance the clock. Timeshifter uses this property of light to time the light exposure advice and ensure that you adapt as quickly as possible to new time zones.